I. Field of the Invention
The present invention relates to an apparatus for expanding and mounting or demounting an annular envelope of a flexible resilient material upon a tire.
II. Description of the Prior Art
In a tire retreading operation, a layer of bonding compound is applied to the buffed tire carcass and the new tread is then applied to the carcass. The tire is then inserted into an annular envelope of flexible rubber or synthetic sheet material which encloses the outer side walls and tread of the tire. The envelope is then sealed to the opposite outer sides of the tire along the tire beads and evacuated so that atmospheric pressure will firmly press the tread against the tire compound while bonding takes place. See U.S. Pat. No. 4,624,732 to King, which discloses an apparatus for sealing such an envelope to the tire and presents a somewhat more detailed description of the function of the envelope.
The envelope in question is of a general configuration similar to that of a tire, except that it is formed of a relatively thin, flexible rubber sheet. Like the tire, the annular envelope has circular openings through its opposite sides whose diameter is approximately equal to the inner diameter of the tire on which it is to be mounted. When mounted upon the tire, the envelope is sealed to the outer side of the tire beads around these openings in the envelope. The remainder of the envelope will loosely encase the tire.
Because the tire must be inserted into the envelope through one of the circular openings in the envelope, and the diameter of that opening is substantially less than the outer diameter of the tire, the envelope opening must be expanded or stretched to accommodate the insertion or removal of the tire into or out of the envelope. While this is frequently done manually, manual mounting and demounting of the envelope is a difficult, time consuming and frequently painful task. Tires most likely to be retreaded are those subjected to heavy duty usage, such as truck tires, for example, and these larger sized tires are more difficult to manually insert or remove from the envelope.
While various machines for mounting and demounting such envelopes on tires have been on the market, they have had but limited appeal to the retreading industry. High cost and operational problems seem to be the major drawbacks.
One such machine presently being marketed includes a hoist from which the tire is suspended in a horizontal (tire axis vertical) position. Below the hoist is a table-like housing having a circular array of articulated fingers mounted upon the top of the housing. After a tire has been manually mounted upon the hoist, the hoist is elevated clear of the fingers which are then located in a radially innermost position. The envelope is then placed on top of the housing. The edges of the uppermost central opening of the envelope are manually engaged with the fingers which are then power retracted radially outwardly to stretch the engaged envelope opening. The hoist is then operated to lower the tire downwardly through the expanded opening into the interior of the envelope. The fingers are then extended radially inwardly, and manually disengaged from the envelope. The enveloped tire may then be removed from the holder. Removal of the envelope is accomplished by reversing the foregoing procedure.
A disadvantage of these previously known tire envelope expanders is the floor space required to accommodate the size of the device.
A further disadvantage of these expander devices is the horizontal orientation of the tire and the envelope. The device forces an operator to lean over the machine in order to mount the envelope onto the envelope applicator.
The present invention is directed to apparatus for mounting and demounting envelopes upon tires which can be produced at a cost substantially less than the machine described above and which performs the mounting and demounting operation in a more efficient manner.